Durable file



United States Patent O 3,531,840 DURABLE FILE Myron D. Tupper, Portland, Norman C. Locati, Lake Oswego, and Curtis L. Graversen, Milwauke, Oreg., assignors to Omark Industries, Inc., Portland, Oreg., a corporation of Oregon Filed Nov. 16, 1967, Ser. No. 683,637 Int. Cl. B23d 71 /00 U.S. Cl. 29-78 4 Claims ABSTRACT OF THE DISCLOSURE A iile is provided with an edge layer of hard metal on the relieved back surface of the file adjacent the outer or cutting edge thereof whereby to provide a hardened and more durable cutting edge. The conventionally manufactured file is iirst coated with a removably adherent coating material, eg. wax, and then a portion of this material on the back surface of each tooth is removed. The iile is then plated with a metal harder than that from which the file was originally formed, the harder metal adhering to the back surface of the teeth adjacent the outer cutting edge. The faces of the tile teeth remain covered by coating material, masking the tooth faces during plating.

Background of the invention Although metal iiles are ordinarily formed from hardened steel, they are nonetheless subject to dulling as a result of Wear or improper use. Heretofore attempts have been made to coat or plate files with a harder metal than that from which the file Was formed, for lengthening the effective life of the iile, causing it to retain its sharp properties over a more extended period of time. However, attempts to plate an entire tile with a hard metal have not been altogether succssful because of a tendency for a rounded edge rather than a sharp edge to form at the outer cutting edge of the iile teeth. The radius of the plating buildup reduces the sharpness and aggressiveness of the tile.

Summary of the invention In accordance with the present invention, a file is plated a hard layer of metal while other portions of the teeth are retained substantially free of such hard metal. The resulting cutting edge of the le is dened at the demarcation between such hard metal and the nonplated portion, and is substantially coincident with the originally manufactured cutting edge of the iile teeth.

According to a preferred method of manufacture, the file is first coated with a removably adherent coating material, and then this coating material is removed from cutting portions of the teeth while being retained at other portions. The file is then coated with a hard metal or plated so that only the portions where the above-mentioned coating material is removed will be plated. Other portions of the iile are masked by the retained coating material.

The removably adherent coating material may be removed by a doctor blade moved along the file from the back towards the face of each tooth whereby the coating material is removed at the back of the tooth, but is retained at the face. Then the iile is treated with a solvent and disposed in a plating bath or the like for acquiring the hardened metal layer at the nonmasked portions of the file teeth.

It is accordingly an object of the resent invention to provide a le having improved durability.

It is a further object of the present invention to provide an improved iile having sharp, hard, and durable outer cutting tooth edges.

The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the Patented Oct. 6, 1970 ICC concluding portion of this specification. The invention, however, both as to organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements.

Drawings FIG. 1 is a longitudinal cross section of a prior art metal iile provided with a plating layer at the left hand portion thereof;

FIG. 2 is a longitudinal cross section of a tile coated with a removable adherent coating material according to a step in the method of making of the present invention.

FIG. 3 is a longitudinal lile cross section illustrating a further step according to the method of making the present invention;

FIG. 4 is a longitudinal cross section of a iile according to the present invention and illustrating yet a further step according to the method of making the present invention;

FIG. 5 is a view of a file partially in cross section with the iile being drawn through an annular shaped doctor blade means according to a step in a method of making the present invention; and

FIG. 6 is a cross section of a iile and doctor blade means taken at 6 6 in FIG. 5.

Detailed description A rnetal iile is usually manufactured starting With steel blank and employing reciprocating chisel means to form a plurality of chisel cuts in the blank defining cutting ridges or filing teeth therebetween. FIG. 1 illustrates a longitudinal cross section of a common iile comprising a central iile body 10 having a plurality of cutting ridges or teeth positioned along the outer edge of the body with each tooth extending across the file generally at an angle to the longitudinal axis thereof. Referring to an individual tooth in FIG. l, a tooth body portion 12 is dened -between a forward cutting face 14 terminating in an outer cutting edge 16, and a relieved back surface 17 extending rearwardly and inwardly frorn the outer cutting edge. The back surface forms or defines an inter-tooth depression 18 where it joins the base of the next rearward tooth face. In use the file is, of course, moved in the direction indicated by the arrow in FIG. 1 with cutting edges 16 engaging a workpiece for removing material therefrom.

Although a file is conventionally manufactured from hardened steel, it would appear logical to provide a harder metal exterior therefor so as to extend the life of the le or extend the period during which its teeth retain their sharpness and effectiveness. FIG. 1 illustrates, at the left hand side of the figure, a portion of a file which has been plated with a hard metal layer 20, as by immersion in a plating bath. Unfortunately, a file plated in this manner has not been found to be nearly as effective as a noncoated iile because the plating causes a somewhat rounded buildup of metal at the outer cutting edge of the file teeth, e.g. at Z2 in FIG. l. This metal buildup increases the edge radius of the outer cutting edge to an extent appreciably reducing the sharpness and aggressiveness of the iile.

According to the present invention, cutting portions of iile teeth are provided with a hard metal layer, harder than the metal from which the le body was formed, While other portions are free of such hard metal layer. The demarcation between the hard metal layer, and portions of the tile teeth where such layer does not appear, defines a substantially sharp cutting edge, rather than a rounded radius as in the case of a completely plated iile. The le is illustrated, for example in FIG. 4, wherein the relieved back surface 17 of each iile tooth is provided with a layer of hard metal 24 extending from outer edge 16 at least part way to depression 18 between the file teeth. The edge of hard metal layer 24 at 1-6 is appreciably less rounded than the radius indicated at 22 in FIG. l., with such outer cutting edge 16 substantially forming an extension of forward cutting face 14. The hardened metal layer 24 is preferably chromium or a chromium alloy and is therefore quite durable and wear-resistant, thereby extending the effective life of the file, with maintenance of the sharpness of the file teeth.

The durable metal layer at the cutting portion of each of the le teeth is desirably formed by first applying a removably adherent coating material 26 to the file as illustrated in FIG. 2. This removably adherent coating material is suitably wax, and may be applied to the file by immersing the same in hot wax or by spraying wax upon the file teeth. The file should desirably ybe thoroughly cleaned before application of the Wax so that the wax will securely adhere thereto. After coating of the file with the wax, a portion of the wax is removed therefrom, and in particular, wax is removed from the cutting portions of the teeth while wax is retained at other portions. Referring to FIG. 3, wax 26 is removed from the relieved back surface 17 of each of the teeth adjacent the location of outer edge 16, while the wax is left in the depression between the teeth, and in particular upon the face 14 of each tooth. Removing the wax or coating material in this manner can be accomplished with a doctor blade brought into relatively moving contact with the file so that relative movement of the doctor blade with respect to the file is along the file and across the teeth thereof. The movement of the doctor blade is from the location of the relieved iback face of each tooth toward the outer edge of the tooth. Such doctor blade is desirably flexible and is urged toward the file so that the relative movement of the file and the doctor blade removes a substantial portion of the coating material or Wax from the file teeth. As the doctor blade engages the tooth, the back surface of each tooth is wiped substantially clean of Wax, but as a consequence of the direction of the relative movement, the doctor blade makes substanitally no direct contact with the faces of the teeth ybut passes over the same.

An example of a preferred doctor lblade arrangement is illustrated in FIG. wherein such blade comprises an annular rubber squeegee 28 held between two annular plates 29 and 30. The squeegee is stationary, and le 32 is moved downwardly, tang end first, through the squeegee annulus so that the squeegee 28 tends to wipe the coating material or wax from the file teeth. In this case, the file is substantially round in cross section, and similarly, the cross section of the squeegee annulus is round to match. It is understood, however, that the squeegee and file may have a triangular, square, or some other similar cross section. Moreover, the squeegee may be substantially linear rather than annular and may be applied to a flat file in a wiping action. The squeegee material is preferably rubber, although some other flexible material may be substituted therefor.

vFIG. 2 illustrates a cross section of a file coated with wax or other coating material before application to the file of a doctor blade of squeegee. FIG. 3 illustrates the same file after application of the squeegee, for example after passage of the file through squeegee 28 in FIG. 5. As illustrated, the wax or other coating material is now substantially removed from the portion of the relieved back surface of the file teeth adjacent the outer edge of the teeth. However, the squeegee will have passed over the wax 26 in the inter-tooth depression, leaving each tooth face 14 covered with wax.

After the removal of the wax from the relieved back surface of the teeth adjacent the outer edge thereof, it will be found that a thin layer of wax will still be adherent to such Iback surface. Therefore, the file is at this time preferably treated with a solvent, with perchlorethylene being preferred in the case of wax. Such solvents as toluene or acetone may also be employed in the case of wax. The file is preferably suspended in the solvent for a period of time whereby the thin layer of wax on the relieved back surface of each tooth is removed, while the wax in the inter-tooth depressions is retained because of its greater thickness. The file may then be briefly immersed in a water solution or the like, and then suspended in a plating bath. For example, a plurality of such les may be placed on racks in electroplating tanks. Electroplating processes are well known, and need not lbe extensively illustrated. Chromium or a chromium alloy is a preferred hard metal material which is applied to the file teeth in such a plating bath. As a result, a hard metal layer 24 adheres to the relieved back surface of the file teeth adjacent the outer edges, and provides a sharp and durable outer edge as indicated at 16 in FIG. 4, rather than a rounded radius as would be the case if the whole file had been plated. The remainder of the file, and in particular the faces of the file teeth, are masked from deposition of the metal because of the location of the remaining -Wax in the intertooth depression. As a result of the inter-tooth retention of wax, the faces of the teeth are substantially free of plating. Therefore the outer cutting edge 16" is a substantial extension of the forward cutting face 14 of each tooth and substantially at the location of former cutting edge 16, the cutting edge being at the demarcation 'between hard layer 24 and the face areas of the teeth which have been masked fro-m deposition of metal.

After the metal layer, 24, is provided for each tooth as illustrated, the remainder of the coating material or wax is removed from the file, for example, by heating, or by suspension of the file in a solvent Abath for a more extended period of time until all of the material 26 is removed. The file then appears as illustrated at the right hand side of FIG. 4.

According to the present invention, a file is provided, the teeth of which are characterized by sharp, hard, and durable cutting edges which are able to retain the quality of sharpness for a more extended period of time than in the case of conventional files.

Although, according to the present invention, the hard metal layer applied to the file has been described as chromium, and the removably adherent coating material has been illustrated as wax, other materials may be substituted therefor. For example, the le may be plated with nickel if desired and/ or a low melting point thermoplastic resin or the like may be used as a removably adherent coating material. Such resin should be workable at room temperature, or at a relatively low temperature.

While we have shown and described preferred embodiments of our invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from our invention in its broader aspects. We therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

We claim:

1. An article of manufacture comprising a metal file having a plurality of teeth each including a body portion having a cutting face terminating at an outer edge and a relieved back surface extending rearwardly and inwardly from said outer edge, said back surface forming an intertooth depression where it joins the face of the next rearward tooth, and wherein said relieved back surface is provided wth an adherent layer including a metal harder than the body of said teeth extending from said outer edge rearwardly at least part way to said depression, said face being substantially free of said layer.

2. The article according to claim 1 wherein said harder metal includes chromium.

3. An article of manufacture comprising a metal file having a plurality of outwardly extending metal teeth each having forward and rearward surfaces which define a body portion therebetween, the forward and rearward surfaces of a given tooth converging to provide an outer cutting edge where the surfaces meet, forward and rearward portions of adjacent teeth forming depressions between said teeth, said outer cutting edges of said teeth each being provided with an adhered hard metal layer including a metal dierent from and harder than the body of said le, for extending the retention of sharp cutting effectiveness of said tile, while other portions of said teeth are free of such hard layer.

4. An artcile of manufacture comprising a metal file including a central file body provided with a plurality of outwardly extending metal teeth, each tooth comprising a body portion extending from said central file body and defined lby the outwardly extending front and rear surfaces thereof which intersect, one of said surfaces being provided with a hard metal layer extending to the intersection with the other surface defining a cutting edge at the outer demarcaion between said hard metal layer and the said other surface, the said other surface being substantially free of said hard rnetal layer adjacent said Cutting edge.

References Cited UNITED STATES PATENTS HARRISON L. HINSON, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated October 6, 1970 MYRON D. TUPPER et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"sucessful" should be --successful;

after "plated" insert --so that the cutting of the teeth are provided with;

"resent" should be -present.

delete second occurrence of "of" "substanitally" should be -substantiallly; second occurrence of "of" should be -or; "depression" should be depressions. "depression" should be -depressions. "artcile" should be -artic1e "demarcation" should be demarcation 'SIGNED ANU QEALEI mm En 'l D. me @omissione-r or Patents- Patent No.

Inventor(s) Column l, line 36, line 43, portions line 66,

Column 2, line 13, line 14,

Column 3, line 40, line 60, line 67,

Column 4, line 2G,

Column 5, line 8,

Column 6, line l,

(SEAL) if? Attest:

EdwardlLFIeherJn USCCMM-DC 603764269 i u,s4 Govtmmnlv rlllmno orrlcr: u o-su-ssc 

